This invention relates to rider rings for a hot displacer in a cryogenic refrigerator. The primary purpose of the rider rings is to maintain a correct positioning of the piston relative to the cylinder wherein the piston is subjected to dynamic loads or forces from the drive mechanism.
Prior art rider rings are normally located in two grooves in the piston. Concentricity problems exist with the use of these rings due to the interaction between the piston, the cylinder and the rider rings. In miniaturized cryogenic refrigerators, the cylinder wall performs the regenerative function so that precise gap control between the cylinder and the piston is required to obtain maximum regenerator performance. Abrasion of the rider rings will result in increased clearances between the hot cylinder and the piston which will affect the regenerator performance.
Resistance to abrasion of the rider ring is also required since the wear particles will tend to clog the regenerator flow passages in both the hot and the cold regenerators.
In prior art devices wherein the rider rings are normally located in grooves, some means must be provided for placing the rings in the grooves. Split rings or sectionalized rings can be used or the piston may be parted at the groove for the rider rings.
These rings also produce acostic noise when in reciprocating motion.